Heating furnaces of the walking beam type are used in the hot rolling process for heating steel materials such as steel pieces or slabs. These furnaces are equipped with skid beams in a plurality of rows for supporting and transporting steel pieces, slabs or like materials to be heated. These skid beams include movable beams and fixed beams. The movable beams periodically repeat an upward and downward movement and a horizontal reciprocating movement, whereby the material to be heated is transported while being transferred to the movable beam and the fixed beam alternately.
FIG. 1 shows a skid beam 1 which comprises a hollow skid pipe 10 provided on the top of its periphery with a plurality of skid buttons 12 arranged axially thereof at a specified spacing. A refractory lining 5 covers the outer peripheral surface of the skid pipe 10 and the base to upper portion of each skid button 12 for use in the interior of the heating furnace. The skid button 12 is a block in the form of a truncated cone, truncated pyramid or the like to support on the top thereof the material 3 to be heated.
Materials heretofore used for skid buttons are heat-resistant alloy steels such as high Ni high Cr alloy steels and high Co alloy steels (e.g., 50 Co--20 Ni--Fe steel).
Cooling water is forcibly passed through the skid pipe to diminish the thermal influence of the high-temperature oxidizing internal atmosphere of the furnace on the skid button and to a the rise in the temperature of the skid button. This assures the skid button of strength capable of withstanding the load of the material to be heated and protects the surface of the skid button from oxidation damage.
However, if the cooling action of the cooling water flowing through the skid pipe is insufficient, the skid button is subject, for example, to deformation or oxidation damage. On the other hand, the cooling action, if excessive, entails the problem that the material to be heated and supported on the top of the skid button is locally cooled by contact with the skid button, which produces a so-called skid mark and permits uneven heating of the material.
Especially recently, it has become common practice to operate heating furnaces at temperatures exceeding 1300.degree. C. to achieve higher operation efficiencies. For operation at such high temperatures, the skid button must be forcibly cooled more effectively so as to be protected from a reduction in strength and increase in oxidation damage. Nevertheless, an enhanced cooling action increases the temperature difference between the interior of the furnace and the skid button, not only aggravating uneven heating of the material as stated above but also entailing a greater heat loss.
Accordingly, skid buttons of conventional heat-resistant alloy have the problem of failing to withstand high operating temperatures and undergoing deformation due to the load of the material to be heated or oxidation damage or the like. Although it has been attempted to use sintered ceramic bodies as skid buttons, ceramics are brittle materials, are therefore liable to crack or chip, and are not usable with good stability.
The present invention has been accomplished in view of the above problems.